The invention relates generally to fasteners and fastener drivers and particularly to those utilizing a retention device to retain the fastener in position for positive engagement into its target location.
It has often happened that a bolt or a screw is required to be inserted into an area that is difficult to access. A retaining device is usually needed to save time and effort to bring the bolt or screw into its target location. In medical surgery, the surgical area in which a bone screw is to be introduced is usually very narrow. It is often difficult to hold the bone screw by hand or by other tool so that the bone screw can be accurately and securely fastened into the targeted area.
There are many prior art screwdrivers which address the aforementioned difficulty in many different ways. These include, but not limited to a magnetized screwdriver, a gripper of different designs and a tubular shaft for guiding the screw.
U.S. Pat. No. 6,189,422 discloses a screwdriver having a retention device capable of retaining a bone screw before inserting the screw into a human or an animal body. The retention device includes a clamping gripper mounted at the distal end of an inner tubular shaft which surrounds the shaft of the screwdriver. An actuation device is provided on the handle of the screwdriver to longitudinally displace an outer tubular shaft so that the outer tubular shaft is moved relative to the inner tubular shaft and over the clamping gripper to close the jaws of the clamping gripper, thereby holding the screw firmly without wobbling. However, the retention device is relatively complicated in terms of the needed disassembly and assembly that is required for disinfection.
U.S. Pat. No. 4,016,913 discloses a holding device comprising a sleeve adapted to fit over the shank of a screwdriver. A pair of diverging arms is mounted at the distal end of the sleeve. A pair of coil springs extending between the diverging arms is adapted to grip the shank of a fastener. Use of bulky items like the coil springs and diverging arms often renders the retention device inadequate for use in a confined space where the fastener is to be located for insertion.
One of the disadvantages of these prior art devices utilizing a gripper is that the gripper can only assume two distinct positions while holding the screw in place in its jaws. The jaws are either open very widely or closed very tightly. The range on the sizes of the screw that can be covered by a specific retention device is limited. The holding strength for retaining or releasing the screw in its place cannot be varied. Moreover, any alignment error of the screw while being held by the gripper cannot be easily corrected.
The screw usually cannot be released gently from the clamping gripper in many of the prior art retention devices.
The retention means of some of the prior art devices for retaining a bolt or screw are quite complicated. The magnetic strength of a magnetized screwdriver is known to decay over time. Furthermore the magnetized screwdriver is often inadequate for some dedicated works, especially for a fastener which is made of a plastic material or of a non-ferromagnetic metal.
Other retention devices are only applicable to some specific applications of introducing a screw for insertion into a workpiece. An object of this invention is to provide a holding device that is simpler in construction, which usually translates into a lower cost of manufacture. Some of the inventive devices described hereinafter can easily be made by molding, further reducing the production cost of the retention device.
Another object is to have a retention device for use with a screwdriver that can be easily assembled and disassembled. A fast disassembly and assembly feature of the retention device is especially important for easy cleaning in medical surgery so that the various components of the retention device and the screwdriver can be thoroughly, readily and quickly sterilized before an operation.
An object of this invention is to provide a means of manipulating the size of the gripping jaw""s opening, thus increasing the range of sizes of bolts and screws the retention device can hold for insertion into a normally inaccessible area of a workpiece. Such a retention device also provides varying strength for holding or releasing the fastener gently.
A still further object is to provide multiple contact points at different parts of the fastener for better screw alignment and improved holding capability, thus further preventing the fastener from dislodging by a sideward displacement during a fastening process. Initial alignment error of the fastener can easily be corrected since the holding strength on the fastener can be varied. The improved retention device is still relatively simple to produce, operate and assemble.
Many of the prior art retention devices are very complicated in design, usually involving many structural components. Some of the retention systems have obvious advantages, however, are expensive to manufacture.
Accordingly, it is the object of the present invention to provide an improved retention device which is simpler to manufacture at a lower cost and easier to operate than the prior art retention means.
The retention device for retaining a fastener comprises an outer tubular shaft slidably disposed upon an inner tubular shaft. Extending from the distal end of the inner tubular shaft is a plurality of resilient gripping members, each having an arcuated section protruding radially away from the axis of the inner tubular shaft. A resilient restraining member mounted on the opposite end of the inner tubular shaft engages an annular flange disposed upon the shank of the fastening tool to prevent the inner tubular shaft from falling off from the fastening tool.
The outer tubular shaft, a portion of which has an inner through bore in a conical shape, is moved along the inner tubular shaft and over the arcuated sections to press in the gripping members to grasp a fastener at the distal end. In another embodiment of the invention, the inner tubular shaft is internally threaded. The holding strength for retaining or releasing the fastener at the distal ends of the gripping members can be gradually varied by rotating the outer tubular shaft with respect to the inner tubular shaft.
In yet another embodiment of the invention, the outer tubular shaft and the inner tubular shaft are both mounted on the handle of the fastening tool for easy handling by simply rotating the outer tubular shaft to engage the fastener for insertion into the workpiece. The fastener can be released gently in a controllable fashion. A simple retention device, comprising mainly an outer tubular shaft and a plurality of gripping members mounted on an inner tubular shaft is also discussed. The device preferably provides a resilient restraining member for engaging either an annular flange on the shank, or an annular recess embedded in the shank, to prevent the retention device from falling off from the fastening tool.
Another retention device, comprising two independent sets of gripping members for use separately in combination with two co-operating outer tubular shafts, is employed to provide multiple contact points at different parts of the fastener, namely at the head and shank of the fastener for better alignment and improved holding capability.